The functions of potassium channels are central to the properties of all excitable mammalian cells. Electrophysiological and pharmacokinetic studies have defined many different classes of potassium channels. However, the molecular basis of this diversity, and the relationships between channel structure and function remain unknown. Through the use of molecular cloning and electrophysiology, we have isolated, characterized, and expressed in frog oocytes a mammalian potassium channel from rat hippocampus. Surprisingly, the properties of this channel do not fit any single kind of channel as defined by classical methods. The major goal of the research proposed here is to further our understanding of the molecular basis of variations among the different classes of mammalian potassium channels. First, we will clone, characterize, and express in frog oocytes mammalian potassium channels, both voltage and ligand gated, with distinct structural and functional properties. The different kinds of channels will be compared to those known by classical methods. Second, structure-function studies, using site directed mutagenesis, will be performed using a range of potassium channels with distinct properties. Site directed mutant studies of whole, reconstructed channels will be conducted in oocytes. Third, ancillary factors which may influence channel functions will be investigated. Fourth, subunit-specific probes will be generated, based on established nucleotide sequences, and employed in in situ hybridization studies to map the expression patterns of potassium channels in the brain. By studying the structure and function of mammalian potassium channels in this way, we hope to answer questions regarding the molecular basis of potassium channel diversity and the significance of this diversity to the basic properties of excitable mammalian cells.